Many structures incorporate a distributed network of sensors in order to successfully fulfill their function. For example, structural health monitoring (SHM) systems may use sensors distributed about a structure. SHM systems can provide the ability to detect and interpret any changes in a structure that may relate to in-use stresses and/or permanent damage thereof. SHM systems may utilize non-invasive detection sensors that are integrated into a structure to continuously monitor components for such changes.
Composite structures are structures consisting of two or more components often with some imparted order which are utilized in a wide variety of applications. For example, air vehicles, such as aircraft, spacecraft or the like, may utilize composite structures in order to take advantage of the benefits attributable to the increased strength-to-weight ratio offered by composite materials. Other applications that may include composite structures include other types of vehicles, such as automobiles, marine vehicles, bicycles and the like, as well as a wide variety of other structures, such as buildings, bridges, etc. Composite structures may also be produced and used with additional functionalities including altered thermal, electrical, acoustical, or mechanical properties by suitably modifying the materials used, the structure itself, or the process used to produce the structure.
Composite structures may be fabricated in various manners designed to impart a predetermined order to a plurality of elements dispersed within a resin or other mostly continuous medium, e.g., polymer, glass, or cement. Typically, a composite structure includes a plurality of structural fibers, such as glass fibers or other elements including carbon fibers, metalized carbon fibers, metal or polymer sheets, carbon or polymer veils, pre-impregnated composite sheets, woven sheets of fibers, mats of random or organized fibers, metal or polymer meshes, embedded in a resin matrix. The resin matrix may be any one of many thermoplastic or thermoset polymer combinations, adhesives or other bonding materials, or cement. Once the composite structure has been laid up, such as by placing a plurality of composite plies one upon another or by laying a plurality of composite tows one beside another, in a manner so as to have the desired shape or woven into a predetermined two-dimensional or three-dimensional structure, the composite structure may be cured, melted or bonded in one or more processing steps.
Implementing an SHM system into a composite structure can provide immediate feedback on in-use stresses and/or permanent damage thereof. However, such a system may add weight and weaken the structural integrity of the composite structure. For example, an SHM system may utilize various sensors (such as strain gauges, thermocouples and optical fibers) permanently mounted in regions of interest. The number and location of these sensors may be limited due to required infrastructure. These concerns may be further exacerbated when the SHM system is operated in a harsh environment, such as the extreme temperatures, shock, vibration and g-loading experienced by aircraft.
Accordingly, there is a need for a structural health monitoring system and methods of forming such system which overcomes the problems recited above.